1. Field of the Invention
This invention relates to an IC chip for wireless identification that is used for identifying various types of objects, persons, and the like, and to methods for reading and writing data from/to the IC chip.
This application is based on Japanese Patent Application No. 2003-319280, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Many kinds of IC cards and IC tags have been developed, and they are widely used for identifying various types of objects, persons, and the like. IC cards and IC tags may be contacting or non-contacting, but the non-contacting type that incorporates an IC chip for wireless identification is superior, since it is more convenient to use. In addition to incorporating the wireless IC chip in an IC card or an IC tag, it may be incorporated directly in various types of objects, including paper money and the like, and used in identifying them.
A conventional wireless IC chip for identification supplies electrical power by using carrier waves from the outside (e.g. see Japanese Unexamined Patent Publication No. 10-145443). That is, when carrier waves from an external reader/writer are received via an on-chip antenna, they are rectified to create an internal power source, so that data that has been superimposed on the carrier waves can be read, and the required data can be transmitted by radio.
According to the conventional art, carrier waves from the outside are used not only in creating an internal power source for the IC chip but also as carrier waves for carrying data; one problem is that, in order to accurately demodulate the superimposed data, the carrier wave frequency must be kept constant, which tends to limit the range of application. That is, since the characteristics of the on-chip antenna mounted on the IC chip are affected by the properties of the item that incorporates the IC chip, fixing the carrier wave frequency makes it necessary to adapt the characteristics of the on-chip antenna to each individual item.